Michael DiBattista

Laser Chemical Vapor Deposition (LCVD) is a high precision, direct-write technique that utilizes beam-stimulated chemical reactions to deposit metals such as Pt or Cu on a micron scale at high speeds. Prior work utilizing a continuous wave (CW) laser has successfully deposited high purity, low resistivity Cu on a multitude of substrates. Unfortunately, CW lasers introduce a significant amount of heat to the substrate, altering interfacial structure and physical properties. Pulsed lasers provide opportunities to minimize heating, but the mechanisms underlying deposition are not well understood. This work compares CW and nanosecond-pulsed LCVD of Cu on Si(100) wherein the laser wavelength is set to 532 nm and copper(I) hexafluoroacetylacetonate trimethylvinylsilane (Cu(hfac) tmvs) is utilized as a precursor gas. Energy-dispersive X-ray spectroscopy and four-point probe methods show low resistivity Cu is produced by both LCVD methods. Finite Element modeling of the laser-induced surface heating that occurs during processing further reveals that LCVD can be accomplished at temperatures well below the Si melt temperature. A new mechanism is proposed for nanosecond-pulsed LCVD whereby the enhanced excitation of conduction electrons near the surface promotes chemical reactions at lower temperatures than that required for CW LCVD.

Reproducible laser-assisted metal deposition with copper hexafluoroacetylacetonate trimethylvinylsilane Cu(hfac) (TMVS) has been demonstrated on a range of relevant semiconductor insulating material surfaces including silicon dioxide (SiO₂), crystalline silicon (c-Si), and organic package material such as polyimide and printed circuit board (PCB) FR- 4. A key to reliable and chemically efficient growth is a novel copper chemistry delivery methodology using direct precursor pulsing. The laser power conditions for deposition are strongly correlated to the substrate material, with increased power for the more thermally conductive samples (0.8 – 1.0 W) and significantly less for packaging materials (50 mW). The laser-assisted copper growth results and material properties are comparable to the published literature. Examples of circuit modifications using this methodology demonstrate its valuable role in the future of circuit edit.

Backside circuit edit (CE) remains a crucial failure analysis (FA) capability, enabling design modifications on advanced integrated circuits. [1-9] A key requirement of this activity is to approach the active transistor layer of the silicon through the removal of the silicon substrate without exposing or damaging critical transistor features. Several methods have been previously developed to enable or assist with the process with either global or locally targeted techniques for thinning the silicon substrate. These methods employ mechanical methods, laser based techniques (continuous or pulsed), or chemical assisted focused ion beam (FIB) etching to accomplish the thinning. Each of these methods presents different strengths and weaknesses, from their reliability to complexity, but very few techniques provide a precise and accurate quantitative measure of the remaining silicon thickness (RST). Here, we will discuss the use of a FIB with XeF2 for backside Si removal, and the development of an in-situ, accurate measurement of RST.

Shrinking transistor geometries present ongoing challenges for backside FIB circuit edit operations. The available space to gain access to critical signal lines has diminished to the order of hundreds of nanometers. Several previous works have shown that the diffusion of active devices can be exposed. This paper explores the effects of exposing and selectively damaging the active diffusion layer of advanced finFET process technology. STEM cross section images show that the devices are unaffected when the silicon substrate is on the order of 1-2ums. When the silicon substrate is removed to less than 100nm, the effect can be seen electrically on a set of ring oscillators.

The efficient passage of electrical current from an external contact to a nanomaterial is necessary for harnessing characteristics unique to the nanoscale, such as those relevant to energy quantization. However, an intrinsic resistance pertinent to dimensionality crossover and the presence of impurities precludes optimal electrical contact formation. In this review, we first discuss the relevant principles and contact resistance measurement methodologies, with modifications necessary for the nanoscale. Aspects related to the deposition of the contact material are deemed to be crucial. Consequently, the use of focused ion beam (FIB) based deposition, which relies on the ion-induced decomposition of a metallorganic precursor, and which has been frequently utilized for nanoscale contacts is considered in detail.

The electrical impedance (both the resistive and capacitive aspects) of focused ion beam (FIB) deposited SiO₂ has been correlated to the specific composition of the ion beam, in Ga- and Xe-based FIB systems. The presence of electrically percolating Ga in concert with carbon (inevitably found as the product of the hydrocarbon precursor decomposition) has been isolated as a major cause for the observed decrease in the resistivity of the deposited SiO₂. Concomitant with the decreased resistivity, an increased capacitance and effective dielectric constant was observed. Our study would be useful to understand the constraints to the deposition of high quality insulator films through FIB based methodologies.

The modern scanning transmission electron microscope (S/TEM) has become a key technology and is heavily utilized in advanced failure analysis (FA) labs. It is well equipped to analyze semiconductor device failures, even for the latest process technology nodes (20nm or less). However, the typical sample preparation process flow utilizes a dual beam focused ion beam (FIB) microscope for sample preparation, with the final sample end-pointing monitored using the scanning electron microscope (SEM) column. At the latest technology nodes, defect sizes can be on the order of the resolution limit for the SEM column. Passive voltage contrast (PVC) is an established FA technique for integrated circuit (IC) FA which can compensate for this resolution deficiency in some cases. In this paper, PVC is applied to end-pointing cross-sectional S/TEM samples on the structure or defect of interest to address the SEM resolution limitation.

A key capability of focused ion beam (FIB) tools is the ability to deposit conductive materials by introducing organometallic precursors such as tungsten hexacarbonyl [W(CO)6] or (methylcyclopentadienl) trimethyl platinum [C9H17Pt]. The FIB deposited metal is often used in applications such as the modification of integrated circuits (ICs) by creating new electrical connection on the device. The electrical properties of the FIB material are of particular concern to high speed digital and radio frequency (RF) circuit designers because the resistivity of the FIB deposited metal is orders of magnitude higher in value than the near bulk resistivity value of the metals used in IC manufacturing. In this paper, we developed a correlation between the chemical composition of the FIB deposited metal and the electrical resistivity using an effective media theory (EMT) model. Analysis shows that gallium from the ion beam is the dominant contributor to lowering the resistivity of the jumper. The results of this work and model allow us to understand the role the chemical elements play in the electrical resistance of the FIB electrical jumper and to estimate the FIB metal resistance from energy dispersive spectroscopy (EDS) analysis and the geometry.

Metal deposition through focused ion beam (FIB) based systems is thought to result in material composed of the primary metal from the metallo-organic precursor in addition to carbon, oxygen, and gallium. We determined, through electrical resistance and chemical composition measurements on a wide range of FIB deposited platinum and tungsten lines, that the gallium ion (Ga⁺) concentration in the metal lines plays the dominant role in controlling the electrical resistivity. Effective medium theory, based on McLachlan's formalisms, was used to describe the relationship between the Ga⁺ concentration and the corresponding resistivity.